Boron alloy steel



Patented Nov. 15, 1938 I z,131,11o

BORON ALLOY STEEL Anthony G. de Golyer, New York, N. Y.

No Drawing. Application July Serial No. 90,001

1 Claim.

The present invention relates to an alloy steel containing molybdenum, boron, zirconium and cobalt, as well as certain other essential alloy components which is particularly adapted for use as metal cutting tools and wear resistant parts.

The types of alloy tool steels, usually classified as high speed steel, which have heretofore been in general use contain tungsten as the principal alloying element; the standard 18-4-1 high speed steel being substantially an alloy of iron with 18% tungsten, 4% chromium, 1% vanadium, 0.50% to 0.75% carbon and minor percentages of other elements, such as manganese, silicon, phosphorus and sulphur. For some uses the composition is varied by increasing or decreasing the percentage of tungsten, or of one. or more of the other elements, In some cases molybdenum or uranium are substituted for a minor portion of the tungsten. Also, cobalt, in amounts from 2% to 8%, is occasionally added.

The improvement of one or more of the important properties and characteristics, as well as economy in the cost of manufacture of high speed steel have been the objectives of extensive research, and various compositions have been suggested. One heretofore proposed composition contains approximately four times as much molybdenum as tungsten; the amounts commercially used usually being from 6% to 8% molybdenum and from 1.5% to 2% tungsten. Another previously proposed composition contains molybdenum as the principal alloying element, and is free from, or substantially free from tungsten.

The class of alloy tool steel containing a higher percentage of molybdenum than tungsten oilers certain manufacturing difiiculties which are well known. One major deficiency of this type of alloy is that molybdenum carbide, the hard constituent of the steel, is readily oxidized at temperatures generated in the tip of high speed cutting tools, or to which the steel is subjected for heat treatment, with the result that the outer portions of the steel are rapidly decarburized. This results in a marked decrease in the hardness of the tool, and a consequent loss of cutting efliciency.

In the heretofore known type of alloy tool steel in which tungsten has been entirely replaced by molybdenum the decarburiz ing action is even more rapid than when a minor percentage of tungsten is present- Furthermore, it has been conclusively determined by investigations extending over a period of several years that the cutting efiiciency of high speed steel containing molybdenum and free from tungsten is, in general appreciably lower than that of the 18-4-1 tungsten type. This is further confirmed by the fact that only a limited quantity of such steels have been used commercially since they were introduced more than ten years ago.- a

The objective of the present invention is to provide an alloy tool steel containing molybdenum and entirely free from tungsten which has advantageous physical properties and characteristics, andwhich possesses a cutting emciency superior 10 to' that of heretofore known alloy tool steels.

I 'have found that by alloying appreciable amounts of boron, zirconium and cobalt in steel containing molybdenum and entirely free from tungsten 'that I can produce an alloy tool steel which is superior to previously known high speed steels. The use of steel of the present invention on numerous and widely varied industrial applications has demonstrated that it is not only fulLv adapted for general purposes but that it is distinctly superior to other heretofore known types of steel for the cutting and working of many metals and alloys under special and diilicult conditions.

I have discovered elements, as herein specified, in the steel results in the formation of hard molybdenum compounds, probably in the nature of complex constituents containing molybdenum, carbon and boron; mo-

lybdenum, carbon and zirconium; molybdenum, boron and zirconium, with or without carbon, or

other complex molybdenum constituents. I have found that such molybdenum constituents are exceptionally stable at temperatures generated in the tips of metal cutting tools operated at high speeds, and at temperatures necessary for thermal treatment of the steel. As a result of extensive research I have found that the presence of appreciable amounts of boron, zirconium and cobalt, as specified herein, in steel containing mo- 40 lybdenum, not only prevents decarburization of such steel during operating and manufacturing operations, but produces a steel having exceptionally high cutting efliciency and strength.

The ease with which molybdenum carbide is to heat treat tools and other articles which have been previously formed to an exact gauge.

by combining the essential 26 Such steel will .the manner and amounts specified herein the present invention are molybdenum, boron, zirconium, cobalt, chromium, vanadium, carbon and iron. Manganese and silicon are usually ,present, but the amount of either of these elements in the steel should not exceed approximately 1%. Likewise phosphorus and sulphur, as well as various other elements commonly found in alloy steels, are present in the nature of impurities incidental to manufacture. It will be understood that the amounts of such impurities present should not exceed the maximum limits usual in alloy tool steels.

Specifically, the alloy of the present invention comprises molybdenum 6% to 16%, boron 0.20% to 2.50%, zirconium 0.25% to 5%, cobalt 2% to 15%, chromium 2% to 6%, vanadium 0.50% to 3.00%, carbon 0.10% to 0.90% and the balance substantially iron.

The results of numerous tests under controlled conditions and in regular manufacturing operations prove that the alloy of the present invention possesses greater cutting efliciency than any previously known high speed steel. For example, tools of this alloy have from 50% to 100% greater cutting efllciency than steels of the 20-4-2, or 18-4-1 types containing cobalt and from 200% to 500% greater cutting, efliciency than heretofore known tool steels containing molybdenum, molybdenum and cobalt, or molybdenum, tungsten and cobalt as the principal alloy components. This outstanding advantage is apparently due to the presence of eifective amounts of boron, zirconium and cobalt in combination with other essential components of the alloy.

Undoubtedly, the chief cause for failure of high speed metal cutting tools, during operation, is

- bined presence of' boron, zirconium and cobalt in the present alloy acts to greatly retard cratering; hence, the cutting tip of the tool is maintained in better physical condition for a much longer period of time than is possible with other alloy steels.

The alloy may be used in the as-cast condition, but inasmuch as it can be readily forged and rolled, I usually prefer to employ it in the wrought condition. Also, the alloy in the wrought condition is particularly amenable to thermal treatment by means of which the hardness and other physical properties and characteristics may be fixed and closely controlled over a relatively wide range.

Although the greatest scope of usefulness for this alloy appears to be in wrought forms as cutting tools, wearing parts, etc., I have found that the alloy is also valuable for welding. That is, the composition may be formed into a weld rod of any suitable type and applied by various means of fusion welding to form. a deposit having substantially the same composition as the original alloy. Such weld deposits may be advantageously used for tips of cutting tools, wearing surfaces and the like; and may be utilized in the as-welded condition, or subjected to suitable thermal treatment before being used.

I claim:

An alloy consisting of molybdenum 6% to 16%, boron 0.25% to 2.50%, zirconium 0.25% to 5%, cobalt 2% to 15%, chromium 2% to 6%, vanadium 0.50% to 3%, carbon 0.10% to 0.90%, the balance substantially iron.

ANTHONY G. D! GOLYER. 

